One of the more contentious debates in the world of avian influenza is over exactly what role migratory birds play in the spread of highly pathogenic H5N1.
Bird enthusiasts and naturalists tend to point to the poorly regulated and controlled poultry trade as being the main source of the spread of the bird flu virus, while those in the poultry industry tend to blame migratory birds.
Over the years we’ve seen study after study that either implicates migratory birds in the spread of the virus, or minimizes their role.
Last September (see Another Migratory Bird Study) a paper appeared in the British Ecological Society's Journal of Applied Ecology, that claimed that the global spread of the H5N1 virus through migratory birds was possible . . . but unlikely.
In a blog from 2009, called India: The Role Of Migratory Birds In Spreading Bird Flu I wrote about an article entitled Scientists rule out spreading of bird flu by migrant birds in India from Xinhua News.
And in January of 2008, Reuters carried a report called:
BANGKOK (Reuters) - There is no solid evidence that wild birds are to blame for the apparent spread of the H5N1 virus from Asia to parts of Europe, Africa and the Middle East, an animal disease expert said on Wednesday.
There was also no proof that wild birds were a reservoir for the H5N1 virus, Scott Newman, international wildlife coordinator for avian influenza at the U.N.'s Food and Agriculture Organization, said at a bird flu conference in Bangkok.
Despite these statements to the contrary, there have been plenty of other reports that strongly associate migratory birds with the spread of the virus.
A few include:
Since I don’t have a bird in this fight, I readily concede that both are probably significant contributing factors in the spread of the virus.
I see no reason why they should be mutually exclusive.
Which brings us to a study that was recently published in PLoS One called:
Wild Bird Migration across the Qinghai-Tibetan Plateau: A Transmission Route for Highly Pathogenic H5N1
Diann J. Prosser, Peng Cui, John Y. Takekawa, Mingjie Tang, Yuansheng Hou, Bridget M. Collins, Baoping Yan, Nichola J. Hill, Tianxian Li, Yongdong Li, Fumin Lei, Shan Guo, Zhi Xing, Yubang He, Yuanchun Zhou, David C. Douglas, William M. Perry, Scott H. Newman
Qinghai Lake in central China has been at the center of debate on whether wild birds play a role in circulation of highly pathogenic avian influenza virus H5N1. In 2005, an unprecedented epizootic at Qinghai Lake killed more than 6000 migratory birds including over 3000 bar-headed geese (Anser indicus). H5N1 subsequently spread to Europe and Africa, and in following years has re-emerged in wild birds along the Central Asia flyway several times.
To better understand the potential involvement of wild birds in the spread of H5N1, we studied the movements of bar-headed geese marked with GPS satellite transmitters at Qinghai Lake in relation to virus outbreaks and disease risk factors.
We discovered a previously undocumented migratory pathway between Qinghai Lake and the Lhasa Valley of Tibet where 93% of the 29 marked geese overwintered. From 2003–2009, sixteen outbreaks in poultry or wild birds were confirmed on the Qinghai-Tibet Plateau, and the majority were located within the migratory pathway of the geese. Spatial and temporal concordance between goose movements and three potential H5N1 virus sources (poultry farms, a captive bar-headed goose facility, and H5N1 outbreak locations) indicated ample opportunities existed for virus spillover and infection of migratory geese on the wintering grounds.
Their potential as a vector of H5N1 was supported by rapid migration movements of some geese and genetic relatedness of H5N1 virus isolated from geese in Tibet and Qinghai Lake.
This is the first study to compare phylogenetics of the virus with spatial ecology of its host, and the combined results suggest that wild birds play a role in the spread of H5N1 in this region. However, the strength of the evidence would be improved with additional sequences from both poultry and wild birds on the Qinghai-Tibet Plateau where H5N1 has a clear stronghold.
The USGS has released a press statement on this study, (which was funded by USGS, FAO, National Science Foundation and the Chinese Academy of Sciences) that describes the project and the results.
New research suggests wild birds may play a role in the spread of bird flu
LAUREL, Md. -- Wild migratory birds may indeed play a role in the spread of bird flu, also known as highly pathogenic avian influenza H5N1.
A study by the U.S. Geological Survey, the United Nations Food and Agriculture Organization and the Chinese Academy of Sciences used satellites, outbreak data and genetics to uncover an unknown link in Tibet among wild birds, poultry and the movement of the often-deadly virus.
Researchers attached GPS satellite transmitters to 29 bar-headed geese – a wild species that migrates across most of Asia and that died in the thousands in the 2005 bird flu outbreak in Qinghai Lake, China. GPS data showed that wild geese tagged at Qinghai Lake spend their winters in a region outside of Lhasa, the capitol of Tibet, near farms where H5N1 outbreaks have occurred in domestic geese and chickens.
This is the first evidence of a mechanism for transmission between domestic farms and wild birds, said Diann Prosser, a USGS biologist at the USGS Patuxent Wildlife Research Center. "Our research suggests initial outbreaks in poultry in winter, followed by outbreaks in wild birds in spring and in the breeding season. The telemetry data also show that during winter, wild geese use agricultural fields and wetlands near captive bar-headed geese and chicken farms where outbreaks have occurred."
Like most scientific studies, this one increments our knowledge, rather than completing it.
While falling a bit short of finding a smoking gun, it documents a plausible mechanism for the H5N1 virus to be spread from domesticated poultry to wild birds during the winter, and from there relayed primarily by asymptomatic birds along the migratory pathways.
The authors conclude by stating:
Our study identifies QHL and Lhasa as important linkages between wild and domestic transmission of H5N1 and provides new supporting information regarding the role of wild birds in long distance spread of this virus.
Further investigation of wild birds and H5N1 transmission within the Central Asian Flyway will increase our understanding of how wild birds may contribute to virus circulation and the unique pattern of outbreaks in this remote region.